The Stromberg Carlson 10 and 11 use special interstage audio transformers to couple a screen grid detector to a pair of 45 grids. A hum balancing arrangement requiring a split secondary is used. Uner present conditions a replacement transformer of that type may not be obtainable, but a substitute can be use if the hum bucking circuit or balancing arrangement is changed slightly. The centertap of the secondary is connected to B- and a 25 ohm wire-wound potentiometer is used for balancing. If the hum is very loud, additional capacitance can be added to the filter system. The value required can be determined by experiment on individual sets of this type. The original circuit is shown in Fig. 1 and the modification in Fig. 2.